Ultrasound scanning system for skeletal imaging

ABSTRACT

An ultrasound scanning system particularly adapted for imaging skeletal structure, such as the spinal column. An ultrasound scanning head for generating ultrasound waves and for receiving reflected ultrasound signals is mounted on a transporter for moving it linearily along the spine between a cervical reference point and a sacral reference point. A position transducer monitors the position of the transducer along the spine and a counter measures the time between the ultrasound pulse and its echo to determine the distance from the transducer face to the tissue interface responsible for generating the echo. The distance and range data is smoothed and analyzed in a digital computer using algorithms that distinguish between the echoes received from bone and other tissue such as lung tissue. The bone data is further processed via computer to produce a visual representation of the spine and rib structure sufficient for the diagnosis of spinal misalignment characteristic of scoliosis.

REFERENCE TO COPENDING APPLICATIONS

This application contains matter disclosed and claimed in the followingcopending applications filed on even date with the present application:

SYSTEM WITH SEMI-INDEPENDENT TRANSDUCER ARRAY, Ser. No. 414,704, by PaulD. Sorenson and Dale A. Dickson;

ULTRASOUND IMAGING SYSTEM, Ser. No. 415,043, by Paul D. Sorenson andLarry A. McNichols;

ULTRASOUND IMAGING SYSTEM FOR SCANNING THE HUMAN BACK, Ser. No. 414,705,by Paul D. Sorenson and Dale A. Dickson; and

ULTRASOUND SCANNER WITH MAPPED DATA STORAGE, Ser. No. 415,044, by PaulD. Sorenson and John D. Badzinski.

APPENDIX CROSS REFERENCE

This application contains an appendix which is a microfilm appendix of atotal of one fiche and fifty-six frames.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention in general relates to the field of ultrasound imaging,and more particularly concerns a system and method for ultrasoundimaging of bony structures such as the spinal column and ribs, whichlends itself to the diagnosis of scoliosis.

2. Description of the Prior Art

Scoliosis is a disease resulting in the deformity of the spine. Thedisorder, which is a significant worldwide health problem, ischaracterized by both lateral curvature and rotation of the vertebrae.The cause of idiopathic scoliosis, which is the most common class ofscoliosis, is unknown, but the symptoms generally appear during thedevelopmental years. Failure to effectively treat the disorder in thosecases where the curvature progressively grows worse leads to deformityof the torso and potentially, cardiopulmonary distress. Patients areoften treated by orthopedic surgeons during the adolescent years ofchildhood by one or more methods which include external orthoticbracing, spinal fusion surgery, and electrical stimulation (internaland/or external) of the paraspinal muscles.

Presently, the most widely used clinical method employed to diagnose,assess, and track the course of the disease is standard X-ray imaging.Since there are no reliable methods yet available to predict the rate ofprogression of the disease, the patient is examined on a regular basis.Typically, a child will be subjected to a large number of X-rays overthe course of the disease regardless of the treatment modalityimplemented. In many cases, no treatment is warranted, out the child isX-rayed periodically to verify that the curve has not progressedsignificantly. It therefore becomes highly desirable to develop atechnique of detecting and monitoring scoliosis which will minimize oreliminate X-ray exposure. In recent years, great emphasis has beenplaced on the need to develop effective, safe methods of screeningchildren in public schools.

Aside from the issue of safety, the X-ray instrumentation currently useddoes not lend itself optimally to the rapid assessment of scoliosis. Forexample, just the right contrast must be obtained and then the equipmentmust be run by a radiological specialist. Further, the orthopedicsurgeon must ponder the X-ray and then perform certain geometricoperations on the image in order to extract quantitative informationregarding the nature of the spinal curvature. Another parameter which isbecoming increasingly important to measure is the amount of vertebralrotation which accompanies the lateral curvature of the spine. This ispresently difficult to accurately assess using X-ray.

Not many alternative means to X-ray for assessing scoliosis appear inthe literature. One method currently under limited evaluation is calledthe Moire technique. This is an optical photographic technique whichdetects bilateral nonsymmetry in the surface features of the back. Themethod employs the principle of interference fringes. The patient's backis photographed through an interference screen or defraction grating.This results in a set of contour-line shadows on the photograph which isindicative of the surface topology of the back. The main shortcomings ofthis system are two-fold. First, there are no established scientificcorrelative studies relating visual surface features to spinalcurvature. Secondly, the device is primarily aimed at screening ratherthan the quantitative assessment of the magnitude of the spinalcurvature. Thus a system and method with which spinal curvature could bedirectly measured which can be repeatedly used without damage to a childor other person would be higly desirable.

SUMMARY OF THE INVENTION

It is an object of the invention to provide apparatus and method forimaging of skeletal structure that overcomes the disadvantages of theabove prior art.

It is an important object of the invention to provide an ultrasoundscanning system including a means for distinguishing between bonestructure and surrounding soft tissue.

It is a further object of the invention to provide an ultrasound systemwhich is particularly well-suited for imaging of the spinal column andthe rib structure adjacent the spinal column.

It is an additional object of the invention to provide an ultrasoundimaging system which provides one or more of the above objects in asystem that can provide a diagnostic image in a single scan.

It is a further object of the invention to provide an ultrasound imagingsystem that provides one or more of the above objects in a system thatprovides data quickly so that it is utilizable in real time by thephysician.

It is another object of the invention to provide a skeletal imagingsystem that is safe and economical so that it can be utilized in regularperiodic treatment of children and other persons.

It is again a further object of the invention to provide an ultrasoundimaging system that provides skeletal representations that are accurateand are easily correlated with established scientific norms.

The invention provides an ultrasound scanning system for skeletalimaging. There is at least one ultrasound transducer for generating anultrasound signal, for receiving an ultrasound signal, and for producingan electrical signal representative of the received ultrasound signal.There is a means for producing a range signal representative of thedistance of objects interacting with the ultrasound signal, and a meansfor producing a position signal representative of the transducerposition. There is a means responsive to the range signal and theposition signal for identifying skeletal structure and for producing anoutput signal representative of skeletal structure.

Preferably, the means for identifying signals indicative of the skeletalstructure and for producing an output representative of the skeletalstructure includes a digital computer. Preferably, the means foridentifying comprises a means for identifying positions at which therange signal changes significantly. In the preferred embodiment of theinvention the means for identifying comprises a means for producing arange as a function of position profile, a means for identifying thepositions in each of the profiles indicative of skeletal structure, anda means for utilizing the identified positions for providing a displayrepresentative of the skeletal structure.

Preferably, the means for producing a position signal includes a meansfor detecting the position of the transducer in relation to apredetermined reference point and preferably the means for detectingincludes a means for referencing the transducer position to at least onepredetermined skeletal reference point.

The preferred scanning system includes a means for movably supportingthe transducer or transducers in relation to the spinal column and ribs.Preferably, there is a plurality of the transducers, and the means formovably supporting the transducers along a vertical line between thecervical reference point and a sacral reference point.

The invention also provides a method of skeletal imaging comprisingdirecting an ultrasound signal through a portion of a body and receivingthe ultrasound signal with an ultrasound transducer while scanning thetransducer over the body portion and determining the position of thetransducer with respect to at least one predetermined reference point toproduce range information correlated with transducer positioninformation, utilizing the range and position information to produce aprofile representing range as a function of position, identifyingpositions in said profile corresponding to skeletal structures, andcorrelating the identified points to produce a skeletal imagerepresentation.

The invention also includes various combinations of the above aspects ofthe invention and numerous other features, objects and advantages of theinvention which will become apparent from the following detaileddescription when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 shows an imaging system according to the invention with thetransducer transport portion of the system in position to image aportion of a patient's ribs and spinal column;

FIG. 2 shows a perspective view of the transducer transport system ofFIG. 1;

FIG. 3 shows a front view of the transport system of FIG. 2;

FIG. 4 shows a cross-sectional view of the transport system takenthrough line 4--4 of FIG. 3;

FIG. 5a shows a cross section of the scanner head taken through line5a--5a of FIG. 3 and showing the transducers pressed against a sectionof the patient's back;

FIG. 5b is a cross-sectional side view of an alternative embodiment ofthe scanner head showing a linear position transducer;

FIG. 6 shows an alternative embodiment of an ultrasound transducer whichmay be used with the system of the invention, which embodiment isreferred to herein as the "roller ball" embodiment;

FIG. 7a shows a front view of an alternative embodiment of thetransducer head which employs three transducers per transducer shoe;

FIG. 7b shows a cross section of one of the transducer shoes of FIG. 7ataken through line 7b--7b of FIG. 7a;

FIG. 8a shows a side view of an alternative embodiment of a portion of atransducer transport system according to the invention;

FIG. 8b shows a top view of the portion of the transport system of FIG.8a;

FIG. 9 shows a partially sectioned side view of an alternativeembodiment of the scanner head;

FIG. 10 shows a front view of a transducer shoe of the embodiment ofFIG. 9;

FIG. 11 shows a block diagram of the preferred embodiment of theultrasound imaging system according to the invention;

FIG. 12a shows the motor control circuit utilized in the embodiment ofFIG. 11;

FIG. 12b shows the electronic circuit of the A/D converter for scannerhead position utilized in the embodiment of FIG. 11;

FIG. 12c shows the electronic circuitry for the transducer drivers andreceivers including the 1 of 16 selector, the received signalmultiplexer and the linear preamp utilized in the embodiment of FIG. 11;

FIG. 12d shows the arrangement of FIGS. 12d.1 and 12d.2 which in turnshow the electronic circuitry for the non-linear time-gain amplifier,including the echo discriminator (rf detector and comparator), utilizedin FIG. 11;

FIG. 12e shows the electronic circuitry for a range counter utilized inthe embodiment of FIG. 11;

FIG. 12f shows the electronic circuitry for a second range counterutilized in the embodiment of FIG. 11;

FIG. 12g (located after FIG. 10) shows the arrangement of FIGS. 12g.1and 12g.2 which, in turn, show the electronic circuitry for thehigh-speed A/D converter and memory buffer system utilized in theembodiment of FIG. 11;

FIG. 12h (located after FIG. 12g on the same sheet of drawings as FIG.10) shows the arrangement of FIGS. 12h.1 and 12h.2 which, in turn, showthe electronic circuitry for the control logic for data expansion whichis part of the high-speed A/D converter and memory buffer systemutilized in the embodiment of FIG. 11;

FIG. 12i shows the block diagram for the microprocessor system utilizedin the embodiment of FIG. 11;

FIG. 13 shows a flow diagram for the preferred embodiment of the methodaccording to the invention indicating the progression of scannerstartup, data acquisition and data processing;

FIG. 14 shows an exemplary profile plotting range versus transducerposition for an embodiment of the invention utilizing sixteentransducers;

FIG. 15 shows an alternative embodiment of the profile of FIG. 14 inwhich the position of the ribs have been identified by circles and theposition of the spinous processes have been identified by squares;

FIG. 16 shows a display representative of the rib and spinal systemformed by connecting the rib and spinal positions determined from thedata of FIG. 15;

FIG. 17 shows an alternative display representing a spinal system formedby connecting the boundaries of rib and spine displayed in FIG. 16; and

FIG. 18 shows the results of performing a medial axis transformation onthe data of FIG. 17 in order to characterize the spinal curvature andspinal rotation associated with the data of FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An exemplary embodiment of the preferred ultrasound scanning system,according to the invention, for skeletal imaging is shown in FIG. 1. Thesystem includes several major subsystems, including a scanner head 10, atransport system 30 for orienting and moving the scanner head in aparticular fashion, a microprocessor-based control and display counsole60, and keyboard terminal 80. The scanner head 10 provides a means ofacoustically coupling low-intensity ultrasound energy to the back of thepatient 11. The transport system 30 moves scanner head 10 in a straightline between two anatomical landmarks--cervical reference means 31 andsacral reference means 32. Control for the scanning process, dataprocessing, record storage, and output of results is provided bymicroprocessor-based system counsole unit 60 which is electricallycoupled to scanner head 10 via flexible electrical cable 61 and totransport system 30 via electrical cable 62. Keyboard terminal 80, whichcan be considered to be part of the system control console 60, providesa means of inputing scanner control commands as well as pertinentpatient information.

In order to clearly illustrate the invention, the descriptipn willcontain three parts. First, a brief description of the mechanics ofultrasound will be presented. Second, a detailed description of thestructure and electronic circuitry of the preferred embodiment will begiven. Finally, a description of the operation of the inventionincluding the method of the invention and the principle features of theinvention will be given.

ULTRASOUND MECHANICS

If a mechanical sound wave in an ultrasonic frequency range (typically 1MHz to 10 MHz) is generated and acoustically coupled to biologicaltissue, the wave will propagate through the tissue at a velocitydetermined by the physical properties of the tissue. Refelections or"echoes" will occur whenever the velocity of propagation of the soundwave is altered. Interfaces between different tissue types within theoverall biological media, in general, present a change in propagationvelocity and hence a portion of the incident energy is reflected. Themagnitude of an echo is proportional to the magnitude of the incidentenergy and the change in velocity at the interface. For example, whenultrasonic energy traveling at 1580 m/s through a layer of muscle tissueencounters bone, the velocity of propagation is increased to 4080 m/sand about 40% of the energy incident on the bone will be reflected inthe form of an echo.

Low power (typically less than 100 mW/cm² average) ultrasound may beeasily generated by the application of a short pulse of voltage (200 Vfor 1 μs typical) to an appropriately constructed piezoelectricalcrystal such as 12 (FIG. 5a). Momentary deformation of the crystal 12ensues and it vibrates for a short period of time at its naturalresonant frequency (2.25 MHz for the present embodiment). Consequently,a low intensity mechanical pressure wave or sound wave is set up in themedia 11 to which the element is coupled.

Conversely, the presence of an incoming ultrasonic wave front in theform of an echo may be detected because the resulting pressure on thecrystal 12 produces a voltage across the crystal 12. Such crystals 12are called ultrasound transducers and the same transducer is typicallyemployed to both transmit and receive pulses of ultrasonic energy.

By aiming the transducer 12 at a target in a particular direction withina defined coordinate system and measuring the time elapsed between thetransmission of a sound wave and the reception of an echo from thetarget it is possible to calculate the distance or range to the target,and subsequently to locate the position of the target within thecoordinate system. Further, it is possible to determine certain featuresof the target (for example surface texture) by analyzing the resultingecho waveform.

In the prior art, medical ultrasound has been employed to examineinternal soft tissue organ structures. Frequently, a "target" structureis treated as a composite of many individual target components. Thepresent disclosure will disclose how the above principles of ultrasoundmay be applied under the management of a microprocessing system toperform a specific type of geometric characterization of the spine andribs.

STRUCTURAL AND ELECTRICAL DESCRIPTION

We now proceed to the detailed structural description of the apparatusaccording to the invention. A perspective view of the scanner 10 and thetransport system 30 for moving the scanner head 10 is shown in FIG. 2. Afrontal view of the same system is shown in FIG. 3 and a cross sectiontaken through lines 4--4 of FIG. 3 is shown in FIG. 4. FIG. 5a shows across section of the scanner head taken through lines 5A--5A of FIG. 3.The transducer shoes 14 of FIG. 3 are omitted in FIG. 5a for clarity.All these figures will be discussed together.

Together the scanner head 10 and the transport system 30 provide a meansfor supporting and moving the transducer 12. In the embodiment shownthere are sixteen tranducers such as 12. Each tranducer, such as 12, isembedded in a transducer shoe, such as 14, which is attached to the endof a movable plunger, such as 15. The scanner head 10 comprises scannerbody 16 having sixteen cylindrical bores, such as 13. Each of the bores13 is of a diameter just slightly larger than the plungers such as 15,and each of the plungers 15 slides within one of the bores such as 13.Within each of the bores, such as 13, there is a spring such as 17, oneend of which seats against the bottom 13A of its respective bore 13 andthe other end of which seats against the end 15A of plunger 15 oppositetransducer 12. A wire, such as 18, is electrically connected to each ofthe transducers, such as 12, and extends through the plunger 15 and bore13 through scanner body 16 into scanner electrical box 19 where they areconnected into the transducer electronics (see below) and ultimately toflexible electrical cable 61.

Scanner transport system 30 includes a frame top plate 31 and a framebase 32 separated and connected by a pair of scanner head rails 33A and33B. Rails 33A and 33B pass through a cylindrical bore within scannerhead blocks 34A and 34B respectively. The bore of blocks 34A and 34B isjust slightly larger than the diameter of rails 33A and 33B respectivelyso that blocks 34A and 34B slide easily on their respective rails.Scanner body 16 is secured to the inner side of blocks 34A and 34B sothat the whole scanner head 10 moves as a unit on rails 33A and 33B. Themajor portions of the drive system 40 for the scanner head 10 is mountedon top plate 31. Drive means 40 includes motor 41 which drives a wormand wheel gear (42 and 43 respectively). Wheel 43 is supported by andlocked to axle 44 which is, in turn, supported on frame 46 and turns inbushings 46A and 46B (not shown) in frame 46. Frame 46 is mounted onplate 31 to support the drive system. Grooved drums 47A and 47B areconnected to either end of axle 44 and turn with the axle 44. A pair ofcables 48A and 48B seat in the grooves of drums 47A and 47Brespectively, pass through holes 35A and 35B respectively in top plate31 and are fastened to pins 36A and 36B set in blocks 34A and 34Brespectively. The other end of cables 48A and 48B pass over guidepulleys 49A and 49B mounted in slots 37A and 37B in plate 31, then passunder pulleys 38A and 38B mounted on the base plate 32 and return upwardto fasten to pins 39A and 39B secured to blocks 34A and 34Brespectively.

FIGS. 8a and 8b show an alternative embodiment of the transport systemwhich may be used if it is desired that the transducers remain tangentto the curvature of the surface of the back. We have foundexperimentally that this is often advantageous in maximizing thereflected energy received and thus maximizing the signal strength fromthe transducers. In FIGS. 8a and 8b the motor and other elements formoving the head are not shown for clarity and as these aspects would besimilar to those shown in FIGS. 1 through 4. This embodiment includes ascanner head 9 having a rotational degree of freedom which permits thetransducer element 149 to be tangent to the surface curvature of back11. Scanner head 9 includes blocks 144A and 144B which slide on rails140A and 140B as described above. Probes 141A and 141B are attached tobrackets on the lower and upper ends of rails 140A and 140B also asdescribed earlier. Blocks 144A and 144B are connected to scanner bodybrackets 144C and 144D respectively by pivot pins 145A and 145Brespectively. Scanner body brackets 144C and 144D are C-shaped bracketswhich fit about the sides of scanner body 142C holding it securely inboth the vertical direction and the direction into the plane of thedrawing, but permitting it to slide in the horizontal direction of thedrawing (FIG. 8a). Y-brackets 142A and 142B are secured (by screws notshown) to scanner body 142C. Rollers 146A and 146B are attached to theends of the "Y" of brackets 142A and 142B by axles 146C and 146Drespectively. Axles 146C and 146D fit within a bore of rollers 146A and146B so that the rollers may rotate freely on the axles. Plungers 147Aand 147B slide within bores in scanner body brackets 144C and 144Drespectively and seat between Y-brackets 142A and 142B and springs 147Dand 147C respectively within the bores. Transducer plungers such as 143are spring-loaded (springs not shown), ride in bores in scanner body142C, and have transducer shoes, such as 148, holding transducerelements, such as 149, mounted on the distal ends of the plungers as inthe embodiments described with reference to FIGS. 2 through 5.

The apparatus described in the preceding three paragraphs comprises ameans for moving the transducers over a field so as to define a plane.The field is the whole 3-dimensional space moved through by thetransducers 12 or 149 as they traverse the back while the plane may beany generalized plane defined by the movement of the transducers. Theplane is generalized in the sense that it may or may not be a flatplane; that is, it may either be the actual "plane" through which thetransducer elements 12 or 149 move, or it may be a plane which isabstracted from the space through which they move. For example in theembodiment of FIGS. 8a and 8b and using the linear position transducersof FIG. 5b, the plane may be a curved surface such as the plane of theback, or it may be a flat plane essentially parallel to the plane inwhich rails 33A and 33B lie. The invention relates to a means forstoring data in array such that the position of the data in the arraycorresponds to the position of the transducer such as 12 or 149 in thisgeneralized plane when the data is produced.

Position tranducer 50 is mounted on top plate 31 and is driven bytransducer drive belt 52 which rotates about position transducer drivepulley 53 which is secured to axle 44 and pulley 54 which is fastened tothe drive shaft of position transducer 50. The position transducer 50 isa potentiometer connected nominally across 0 to 12 volts d.c. (typicaloperating range 2-8 volts d.c.). As pulley 54 turns, a wiper within thepotentiometer 50 moves and produces a voltage proportional to thedistance which the scanner head 10 has moved. Wires 55 which carry theoutput signal of position transducer 50 and wires 56 which carry theinput current to motor 41 form flexible electrical cable 62 (FIG. 1).

Located on the transducer support system 30 are means 57 for referencingthe ultrasonic transducer position to a cervical reference point and ameans 58 for referencing the ultrasonic transducer position to a sacralreference point. Each of these reference means includes a bracket suchas 59A which supports a push rod, such as 59B which is mounted in a holethrough bracket 59A. A spring 59C seats between one side of bracket 59Aand a cap 59D mounted on the end of push rod 59C. Together the referencemeans such as 57, scanner head 10, the cables such as 48A, drums 47A,axle 44, drive pulley 53, drivebelt 52 and position transducer 50provide a means for producing a position signal representative of theposition of transducer 12.

FIG. 5b is a cross-sectional side view of an alternative embodiment ofthe scanner head. In this figure the transducer shoe is again not shown.This embodiment includes a linear position transducer 20 which producesa signal proportional to the position of plunger 21. Linear positiontransducer 20 includes a contact 22 secured on the bottom side ofplunger 21 and extending a small distance beyond the side of the plunger21, and a resistance element 23 embedded in scanner body 24A with itssurface exposed along a section of bore 24B so that contact 22 movesalong resistance element 23 as plunger 21 moves in bore 24B. Wire 25A isattached to contact 22 and wire 25B is attached to one end of resistanceelement 23 and both wires 25A and 25B are input to an A/D converter 26to complete a circuit through resistance element 23. The voltage throughthe linear transducer circuit 20 is proportional to the position ofcontact 22 on resistance element 23 and thus is a measure of theposition of plunger 21 and ultimately of the position of transducer 28.The A/D converter translates the voltage to a digital signal in a mannersimilar to that described below with reference to FIG. 12b. The digitalsignal is input to the control console 27 for use as will be discussedbelow.

Note that wires 18 (in FIG. 5a) and 24A (in FIG. 5b) are shown straightonly for clarity. In actuality they are coiled in the bore so that theymay extend and contract as plungers 15 and 21 move.

FIG. 6 shows an alternative embodiment of the ultrasonic transducer 100applied to surface of body 101. Transducer 100 comprises casing 104,roller ball transducer 105, ultrasonic lens 106, internal transducerelement 107, transducer support rod 108, transducer supporting bracket109, transducer leads 111, gel inlet port 112 and tubing 114. Casing 104includes forward member 102 which widens as it progresses towards rollerball 105 and has a bearing surface 103 shaped as a portion of a sphereof a radius just slightly larger than the radius of roller balltransducer 105. The relative sizes of roller ball transducer 105 andspherical surface 103 are such that roller ball 105 will turn in bearing103 as transducer 100 is moved along the surface of body 101 with rollerball 105 in contact with body 101, and such that a film of gel coveringthe surface of roller ball 105 will pass through the gap between surface103 and the surface of roller ball 105. Port 112 comprises a hollowcylindrical tube extending a short distance above the surface of casing104. Rubber tubing 114 has an internal diameter such that it fitstightly about the external diameter of port cylinder 112, and connectsto a source of ultrasonic gel (not shown). In operation gel fills theinterior 115 of ultrasonic transducer 100. Support bracket 109 is awasher-shaped member having holes such as 117 which permit the gel topass freely through it.

FIGS. 7a and 7b show another alternative embodiment of the transducershoe. FIG. 7a shows a front view of four shoes with the gap indicatingthat additional shoes may be inserted; in the case of the preferredembodiment there are sixteen such shoes. Each shoe, such as 120,includes a shoe body 121, transducer housing, such as 122 in which threetransducer crystals, such as 123, 124, and 125 are embedded. Each shoe120 is supported by a hollowed cylindrically shaped transducer rod 127which fits into a bore 128 formed in the rear of the shoe body 121.Wires 130, 131, and 132 pass through a hollow 133 formed in shoe body121 and through rod 127 to connect each of transducers 123, 124 and 125to the transducer electronics (not shown) as discussed above. Transducerhousing 122 is embedded in shoe 121 at an angle so that there is aslight bit of overlap in the vertical plane between the individualtransducer crystals, as for example, between crystal 123 and 124.Further, each individual shoe, such as 120, has the top portion of theshoe, such as 121A, offset from the bottom portion of the shoe, such as121B, so that the top portion of each adjoining shoe overrides thebottom portion of the next shoe, as for example, top portion 138A ofshoe 136 overrides the bottom portion 121B of shoe 120. The overridingis such that the last transducer in one shoe has the same overlap withthe first transducer of the next shoe as the individual transducers ineach shoe have, as for example, transducer crystal 125 in shoe 120overlaps with transducer crystal 137 in shoe 136. The advantages of thisarrangement of transducers and transducer shoes will be discussed below.

FIGS. 9 and 10 show a third alternative embodiment of each transducershoe and another alternative embodiment of the scanner head whichincorporates an automatic gel-spreading system. This transducer systemincludes a single transducer crystal 150 embedded in shoe housing 151which is supported by cylindrical rod 152 which fits into a bore 153 asdiscussed above with respect to the previous embodiment. It alsoincludes transducer wire 154 which passes through a bore 155 in the bodyof transducer shoe housing 151 to connect transducer crystal 150 totransducer electronics (not shown) as previously discussed. The upperand lower edges 157A and 157B of housing 151 are rounded and smooth. Theshoe housing 151 has an internal passage 160 which connects tubing 167and shoe reservoir 161. Reservoir 161 communicates with trough 165 inthe exterior face of shoe housing 151 through a series of openings suchas 163. The lip 166 of trough 165 is also rounded and smooth.

Support rod 152 fits in a cylindrical bore 168 formed in scanner body169. In this embodiment, gel source 170 is formed in the top of housing169. Source 170 includes gel tank 172 and gel pump 175. Gel tank 172 hasa cylindrical inlet port 176 which is threaded on its outside surfaceand which is normally covered by removable threaded cap 177. One-wayvalve 178 communicates between the interior 179 of tank 172 and pumpchamber 180. Outlet port 182 which is a short, hollow cylindercommunicating with pump chamber 180 has an outlet one-way valve 183which controls flow through the outlet. Tube 167 fits about the outerdiameter of cylindrical port 182. Servomotor 185 drives screw 186 whichis attached to piston head 187. When piston head 187 moves to the rightin the drawing one-way valve 183 closes and one-way valve 178 opens topermit gel to flow from tank 172 into pump chamber 180. When piston 187moves to the left, one-way valve 178 closes and one-way valve 183 opensto permit the gel to flow through tube 167 into reservoir 161 and outinto trough 165. Servomotor 185 is electrically connected to, andcontrolled by microprocessor 190. Position transducer 191 measures theposition of scanner head 148 (see the discussion of the precedingtransducer of FIGS. 2, 3 and 4 above). The signal from positiontransducer 191 is fed through A/D converter 199 into microprocessor 190so that the microprocessor regulates the speed of servomotor 185, andthus the gel flow into trough 165, with the motion of scanner head 148,and thus the motion of trough 165 over the surface of the body.

FIG. 11 shows a block diagram of the electronic system utilized in theembodiment of the invention shown in FIG. 1. The electronics included inscanner head 10 is enclosed in the dashed rectangle. In this diagram thetransducers are indicated as T₀, T₁, T₂, . . . T_(I). . . T_(N-2),T_(N-1) for purposes of the generalized discussion below. In thepreferred embodiment there are sixteen such transducers and thus, N isequal to 16. The transducer driver and receiver circuitry 71 deliverssignals to and receives signals from the ultrasonic transducers 70. Oneof sixteen selector circuitry 72 receives signals from themicroprocessor system 75 and in turn, applies signals to the transducerdrivers and receiver circuitry 71. Received signal multiplexer 73receives the signals derived from the reflected ultrasonic waves fromthe transducer driver and receiver circuitry 71. A signal from themicroprocessor system 75 is applied to received signal multiplexer 73 toinform it which signal should be recognized. The signals recognized bythe received signal multiplexer 73 are passed to the linear preamp 74and, after amplification, proceed on to the nonlinear time-gainamplifier 76. The doubleline 77 indicates a mechanical linkage betweenthe motorized mechanical transport system 78 and the ultrasonictransducers 70. As discussed above, there is also a mechanical linkagebetween motorized mechanical transport system 78 and position transducer79. The signal from position transducer 79 is applied to position A/Dconverter 81 and the digital output from the position A/D converter isapplied to the microprocessor system 75. The microprocessor system 75applies a clock signal and a start signal to range counters 82. Theoutput of the nonlinear time gain amplifier 76 is applied to echodiscriminator 83, and when an echo is detected, a signal is applied tothe stop input of range counters 82. The signal from the range countersis applied to the microprocessor system 75. In this embodiment themicroprocessor 75, the range counters 82, and the echo discriminator 83together comprise a means for providing a range signal representative ofthe distance of objects interacting with the ultrasound signal. Themicroprocessor system 75 provides an output to the display system 84.High-speed A/D converter and memory buffer system 85 is an optional partof the system which will be discussed below. This system 85 receivessignals from nonlinear time-gain amplifier 76 and microprocessor system75; these signals are indicated by dotted lines to indicate they areoptional. The signal from high-speed A/D converter and memory buffersystem 85 is applied to microprocessor system 75.

FIGS. 12a through 12h show details of the circuitry of each of theportions of the circuitry shown in FIG. 11. With the exception of thetime-gain amplifier the particular elements of the subcircuits are forthe most part conventional and those skilled in the art will be able todevelop such circuits and alternatives to such circuits from thedescription given and standard electronic literature. The various partsused and sources for those parts will be presented in order to fullyelucidate the construction of the invention.

The motor control circuitry is shown in FIG. 12a. In this figure, andthe subsequent figures showing electronic circuitry, standard electronicsymbols for the various circuit elements are used. Each of theseelements will be pointed out in the first figure in which they areencountered. In FIG. 12a, a resistor is shown at 78A, with the value ofthe resistor given in ohms alongside the resistor. A transistor is shownat 78B, with the standard trade designation for the transistor typegiven alongside the transistor (MJ4032 for transistor 78B). A capacitoris shown at 78C with the value of the capacitance, 0.01 μf, given nextto the capacitor. A field effect transistor (FET) is shown at 78D, withthe standard trade designation of the FET type, 2N6660 given next to theFET. The symbol at 78E, shaped like the tail of an arrow, indicates aconnector. The number next to the connector symbol, such as J1-30 at78E, indicates where the connection is to be made. For example, theJ1-24 at 72B in FIG. 12c is connected to the J1-24 connection at 76A inFIG. 12d. Furthermore, all such symbols which begin with a J1, J2, or J3designation refer to standard connection points on an ISBC 80/30 singleboard computer (microprocessor system) made by the Intel Corporation,3065 Bowers Avenue, Santa Clara, Calif. 95051. Triangles, such as 78F,indicate a digitial signal ground, while small circles, such as at 78Gindicate a plus or minus voltage connection. The voltage is given nextto the circle, either as a plus or minus numerical voltage or as Vcc₁ orVcc₂ which indicate positive DC power supply voltages. Normally Vcc₁would be set at +12VDC and Vcc₂ would be set at +5VDC. The highervoltage (Vcc₁) runs the motor while the scanner head is being raised orreturned to the ready position while the lower voltage Vcc₂ is switchedto when the scan is being conducted. This saves time during the returnof the scanner head. The circuitry for the position A/D converter forthe scanner head position is given in FIG. 12b. The large rectangle 81Ais an analog-to-digital converter chip such as that made by AnalogDevices, Inc., Route 1, Industrial Park, P.0. Box 280, Norwood, Mass.02062. The designation for this chip and other chips used in theelectronics is shown in the rectangle. At 81B a variable resistance isshown, with the maximum value of the resistance (100 Kohms) given nextto the symbol. The symbol at 81C indicates a potentiometer with themaximum value of the resistance of the potentiometer (20 Kohms) givennext to the symbol for the potentiometer. The 1 Kohm potentiometer at81D is the potentiometer within the position transducer 50 in FIG. 2.

The electronic circuitry for the one of sixteen selector, the transducerdrivers and receivers, the received signal multiplexer and the linearpreamp are shown in FIG. 12c. The one of sixteen selector circuitry isessentially contained in integrated circuit chip 72A. This is a standardintegrated circuit chip which may be purchased, for example, from RCASolid State, Box 3200, Summerville, N.J. 08876. Symbol 71A represents asignal diode, with the standard trade designation for the diode givennext to the symbol. 71B is an inductance with the value for theinductance given next to the symbol. Transducer 71C is a 2.25 MHztransducer produced by Harrisonics of Stamford, Conn., 06902. Receivedsignal multiplexer is also essentially contained in an integratedcircuit chip 73A with the standard trade designation number given on thechip. Symbol 74A in the linear preamp circuit represents an operationalamplifier, such as that produced by National Semiconductor Corporation,2900 Semiconductor Drive, Santa Clara, Calif. 95051. The transducerdrive and receiver circuitry shown at 71D is reproduced sixteen times,once for each transducer in the preferred embodiment and each of thesixteen circuits is connected between selector 72A and multiplexer 73Aas indicated by the dotted lines in the drawing. The WW designationgiven at point 74B indicates a wire connection to the terminal labeledWW at 76C in FIG. 12d.1. Likewise, other points with double lettereddesignations elsewhere in the drawings indicate wire connections betweenidentically labeled points.

The nonlinear time-gain amplifier and echo discriminator are shown inFIGS. 12d.1 and 12d.2. The two figures should be placed side-by-side asshown in FIG. 12d and are connected along line 76A. In FIG. 12d.1 theonly new symbol introduced is shown at 76B. This is a dual gate FET, andthe standard trade designation for the FET is given just near thesymbol. The echo discriminator circuitry is shown in FIG. 12d.2. Thisincludes an RF detector and a comparator as shown. The three transistorsand diode indicated by 83A are formed in a single standard chip with thetrade designation CA3146. All other elements in the circuits have beenpreviously described.

The first of two range counters is shown in FIG. 12e. This circuitincludes four NAND gates, such as 82A, six NOR gates, such as 82B, andan inverter shown at 82D. The four gates designated CD4011 are containedin a single integrated circuit package, as are the four gates indicatedby the designation CD4001 and the two gates and inverter indicated bythe designation 4000. 82E is a binary counter, with the standard tradedesignation indicated on the drawing.

The circuitry for a second range counter is given in FIG. 12f. Thiscircuitry includes four AND gates 82F. Element 82G is a flip-flop, withthe standard designation for the flip-flop given on the drawing. The ORgates, such as 82H are located on a single standard chip. The circuitryfor the optional high-speed A/D converter and memory buffer system isshown in FIG. 12g.1 and 12g.2. These figures should be arranged as shownin FIG. 12g (located after FIG. 10) and when this is done, theconnections between the two parts of the circuitry along line 85A isclear. Symbol 85R indicates an analog signal ground. Digital signalgrounds and analog signal grounds are maintained separately in thesystem. The principal parts of this system include the A/D converter85B, model TDC1007PCB manufactured by TRW, Inc. 10880 Wilshire Blvd.,Los Angeles, Calif. 90024 and the model TC1006 high-speed shiftregisters, such as 85C, also manufactured by TRW, Inc. Symbol 85Drepresents a standard type BNC connector. In FIG. 12g.2, 85E is ahigh-speed D/A converter built by TRW (model TDC 1016), and 85F is anoperational amplifier with the standard designation LM10 such as may bepurchased from National Semiconductor Corporation at the address givenabove. The control logic for utilizing the high-speed A/D converter andmemory buffer system in the data expansion process (which will bediscussed below) is shown in FIGS. 12h.1 and 12h.2. These two drawingsshould be arranged as shown in FIG. 12h (located on the same sheetdrawing as FIG. 10), and when this is done the electrical connectionsbetween the two figures along line 85H is evident. In FIG. 12h.1 thetriangles 85I are SN7407 drivers, such as those available from SigneticsCorporation, 811 E. Arques, P.0. Box 9052, Sunnyvale, Calif. 94086. Thearrow heads, such as 85J indicate connections to other points in thedrawing with the same designation for example, connector 85J connects tothe CL5 connector 85G in FIG. 12g.2). The arrow head indicates thedirection of signal flow. Rectangle 85K represents a 93L10 typesynchronous four-bit decade counter, such as that available fromNational Semiconductor Corporation at the address given above. 85L is a10 MHz crystal available from International Crystal Mfg. Co., Inc., 10GNorth Lee St., Oklahoma City, OK, 73102. Rectangle 85M is a type CD40103down counter and 85N is type CD4098 dual monostable multivibrator bothof which are available from RCA Solid State. FIG. 12h.1 also contains aseries of switches such as 85P, which are conventional single-pole,single-throw switches. The circuit of FIG. 12h.2 contains four type 8216four-bit bidirectional bus drivers, such as 85Q, available from theIntel Corporation.

The block diagram of the microprocessor and display system is shown inFIG. 12i. The heart of the system is an Intel 8085 processor chipincorporated on an Intel ISBC 80/30 single board computer 75A, and anIntel ISBC 116 memory board 75B. This computer system is connected withthe scanner head and echo processing electronics 90 as discussed above.For data storage, computer 75A communicates with Intel ISBC 204 diskcontroller 75C which, in turn, communicates with a Shugart SA-400mini-floppy drive 75D, available from Harold E. Shugart Company, Inc.,1415 Gardena Avenue, Glendale, CA 91204. The display system includesthree Matrox MSBC-512 graphic display boards such as 84A, a MatroxMSBC-2480 alpha display board, 84B. The display system includes an AxiomEX-850 printer 84C, and a Ball TV-120 display 84D which includes cathoderay tube 65. The Matrox display boards can be obtained from Matrox Ltd.,2795 Bates Rd., Montreal Quebec, Canada, the Axiom printer is availablefrom Axiom Corporation, 5932 San Fernando Road, Glendale, CA 91202, andthe Ball display is available from Ball Electronic Display Division,P.0. Box 43376, St. Paul, MN, 55164. The disp1ay boards such as 84A and84B receive inputs from the computer 75A and communicate with each other(arrows). The Alpha display board 84B receives input from the keyboard80 and applies a signal to computer 75A. Keyboard 80 is a Cherry570-61AA keyboard available from Cherry Electrical Products Corporation,3625 Sunset Avenue, Waukegon, IL 60085. The system just described,including computer 75A, Memory 75B, controller 75C, display boards, suchas 84A and 84B, minifloppy drive 75D, printer 84C, TV display 84D andkeyboard 80, when programmed with the software described below, comprisea means responsive to the range signal and the position signal foridentifying signals indicative of skeletal structure and for producingan output representative of skeletal structure.

The materials out of which the invention is constructed are, for themost part, obvious from the functions performed, however, these will bebriefly described for completeness. Rails 33A, 33B, 140A and 140B arepreferably made of stainless steel, while plates 31 and 32 and frame 46are made of aluminum, although any suitable metal or hard plasticmaterial may be used. Wheels and pulleys, such as 47A, 49A, 38A, 53, 54,146A and 146B may be made of a machineable plastic such as Teflon®,although any other suitable plastic, metal or other material may beused. Likewise, blocks 34A, 34B, 144A, 144B, 144C and 144D and thetransducer housings such as 14, 121, 148 and 151 may be made of Teflon®,or similar plastics, fibers or metals. Rods such as 15, 127, 143, 147Aand 152, the scanner head bodies such as 16 and 142 and gears such as 43and 42 may be made of brass or any other suitable metal or plasticmaterial. Springs such as 17, 59C, and 147C, as well as cables such as48A may be made of stainless steel or any other suitable metal,compressed fiber, etc. Brackets 59A, 144C and 142B and rod 59B may bemade of aluminum, Teflon® or any similar metal or plastic while tip 59Dmay be made out of rubber, silicone rubber, or other plastics, fibers,etc. The transducer elements such as 12, 107, 123, 149 and 150 may bemade of barium titanate (referred to as K-85 ceramic by Harrisonics,Inc.). Roller-ball transducer 105 and lens 106 may be made of acrylateplastic or any other suitable plastic or metal. Housing 104 (FIG. 6) and172 (FIG. 9) may be made of ABS plastic or any other suitable plastic ormetal material, preferably one that is injection moldable. Rod 108 andbracket 109 (FIG. 6) may be made of Teflon® or any other suitableplastic or metal, etc. Screw 186 and piston head 187 may be made ofbrass, stainless steel, ABS plastic or other suitable material. Tubes114 and 167 may be made of silicone rubber, polyurethane or any othersuitable flexible rubber, plastic or other materials. Resistance element23 may be made of carbon or any other suitable resistor material.

FEATURES AND OPERATION

To perform a typical back scan a start command is entered via theconsole keyboard 80. The transport motor 41 elevates the scanner head 10to the top of the transport rack 30. The transport rack 30 and scannerhead 10 are then appropriately oriented on the back 11 of the patient(the patient may be in the standing or prone position) with the cervicalreference point 31 and the sacral reference point 32 contacting twowell-known palpable anatomical landmarks of the spine such as C-7 andthe sacral crest or coccyx. The procedure of aligning the upper andlower reference points 31 and 32 of the transport rack 30 with the upperand lower landmarks of the spine also places the transducers 12 of thescanner head 10 in positive contact with the skin on the back 11 of thepatient. The unique method of maintaining this contact for the durationof the scan is described in detail later in a section on the scannerhead.

Following a momentary delay, the ultrasound transducers 12 in thescanner head 10 begin to sequentially emit pulses or bursts ofultrasound energy. Suppose that the "N" number of transducers in thearray 70 (FIG. 11) are numbered from left to right as T₀, T₁, T₂, . . .T_(I). . . T_(N-2), T_(N-1), where I is the number of any arbitrarytransducer in the array. T₀ first acting as an acoustic generator ortransmitter emits a short pulse of sound or is said to be "fired."Immediately thereafter, T₀ is switched to a receiving mode. As the soundenergy propagates through the tissues of the back, the interfaces ofvarious tissue layers cause some sound energy to be reflected in theform of echoes. T₀, therefore, listens for a prescribed time period anddetects any echo in this "window" of time. The echo signals areprocessed in a prescribed fashion by the scanner head electronic module19 and by the system console 60 as described in detail later. T₁ thenfires and begins listening, and so on, until T_(N-1) has fired andlistened. Following completion of this firing and listening sequence,the process is repeated for N transducers in periodic fashion.

Coincident with the transmitting and receiving activity of thetransducers, the scanner head 10 moves mechanically away from thecervical reference point toward the sacral reference point. The "field"over which the transducer array scans has dimensions of "X" units wideby "Y" units in length. The computer software is configured such that amemory matrix is defined with "J" referring to rows and "I" to columns.The number of columns corresponds directly to the number of transducers(N) in a row across the scanner head 10. N will be set equal to 16 forpurposes of example. The number of rows is equal to a selected number ofequal subdivisions (J) in the length (Y) of the scan field. The numberof rows will be selected as 480 for further illustration. The scan fieldmay then be represented by a (J, I) matrix of 480×16 or 7680 discretepoints. In general, a short burst of ultrasound energy is introduced atleast once in methodical fashion at each one of these points in thefield of scan and the resulting echo pattern or echo signature isanalyzed at each point.

At each point in the field of scan, any echoes occurring arediscriminated for selected features by an echo discriminator 83.Calculation of the range or distance between the transducer face and therelevant anatomical structure which produced a discriminated echo at aparticular (Y, X) coordinate is performed. Each piece of rangeinformation is stored in the corresponding element in the (J, I) memorymatrix. Range then becomes a third dimension and is directly related to"Z", the dimension of depth into the back at which the tissue interfaceproducing the discriminated echo is located.

The ramification of this scanning process is that following theapplication of a one pass linear scan down the back there arepotentially 7680 numbers contained in a memory map which may besubsequently rapidly processed to render information on the geometricalrelationships between the various components of the dorsal skeletalsystem.

One important use of this information is to determine the presence orabsence of abnormal lateral curvature of the spine (scoliosis) and,further, to automatically assess the severity or "degree" of suchabnormal curvature. This is made possible by constraining the transducerarray 70 to move in a well defined manner, namely a straight line,between the cervical and sacral reference points. The lateral curvatureof the spine may then be referenced to a straight line drawn betweenthese two points--two points through which the spine must passregardless of its geometry between these two points.

Integrated into the design of the system console 60 are means ofvisually or graphically communicating results. These means include acathode ray tube (CRT) 65 and a graphic paper printer 84C to produce ahard copy of any image appearing on the face of the CRT 65. Alsoincluded in the scanner console 60 is a "mini-floppy" magnetic discsystem 75D. This facilitates the storage of clinical results on a largenumber of patients combined with patient history information.Acquisition, retrieval and management of all data is facilitated byfingertip control at the console keyboard 80.

Before proceeding with a discussion of the configuration and operationof the ultrasonic scanning system it is appropriate to discuss thefeatures of the scanner head 10 and the mechanical system 30 whichsupports and transports the head. The concept of the scanner head 10 isperhaps best illustrated by FIGS. 3 and 5. One unique feature of thissystem is that the individual transducer elements 12 are affixed toplungers 15 which have one degree of freedom of movement, but may moveindependently of one another. Each plunger/transducer combination isspring loaded within a common housing 16 to all plungers 15 such thatwhen the assembly 10 is pressed against the back of a patient eachtransducer 12 provides positive compression against the skin 11. As thescanner head 10 is then moved over a complex plane of body curvaturesuch as the human back each transducer 12 independently tracks thecurvature such that positive acoustic coupling is maintained for eachactive element in the scanner head 10.

An alternative embodiment of the scanner head is shown in FIGS. 8a and8b and has been described above. This embodiment has an additionalrotational degree of freedom of movement that allows it to adjust to thecurvature of the back so that the face of the transducer elements, suchas 149, are tangent to the surface of the back 11.

As the transport system is brought to the patient's back such thatlandmarks X and Y are located and are contacting landmark probes 141Aand 141B, transducer shoes 148A seek positive skin contact as beforebecause of spring loading pressure on plunger 143 relative to housing142C. In position No. 1 of FIG. 8a, assume roller 146B contacts thepatient's back before roller 146A. Because of positive pressure causedby springs 147C and 147D, the transducer array rotates counter-clockwiseabout roller axle 146D. Simultaneously housing 142 rotates about pivots145A and 145B until roller 146A is in positive contact with patient'sback 11. The system is now in equilibrium with the transducer elementface 149 parallel to line aa'. Because of the geometry of construction,line aa' is a very close approximation, if not exact, tangent at point"A" to the average curvature of the back 11 between rollers 146A and146B.

In operation, then, as the scanner head 9 descends (preferably undermotor power) along transport rails 140A and 140B, rollers 146A and 146Bare forced to maintain positive skin contact with the patient's back 11.Angle φ, in general, varies to maintain the tangential curve trackingsituation. Position No. 2 simply depicts the position of the system asthe head 9 nears the end of its downward movement. Here the point ofcurve tangency is at point "B."

The linear position transducer 20 shown in FIG. 5b may be used incombination with either of the plunger systems described above. In thoseembodiments which employ linear position transducer 20, one such linearposition transducer 20 is an integral part of each independent plunger15. The output of the linear transducer is used to make corrections inthe computed range values as shall be described below.

Also shown in FIG. 2, or FIG. 7a or FIG. 9 is the detail of varioustransducer shoes 14, or 121, or 151 respectively which are contouredassemblies into which the transducer elements 12 fit. As previouslymentioned, transducer shoes are not shown in FIGS. 5a or 5b for clarity.The shoes 14, or 121, or 151 prevent the conventional transducerelements from gouging into the skin 11 of the patient as the scannerhead 10 moves. The shoes 14, 121, or 151, greatly alleviate thisdiscomfort.

An alternative to the shoes 14, 121, or 151 on the nose of thetransducers is the "roller-ball" transducer element shown in FIG. 6.This transducer solves two problems simultaneously. First, the sphericalrolling ball 105 effectively eliminates the sliding friction andsubsequent gouging of the patient's skin 101. Secondly, the roller ball105 automatically dispenses the proper amount of a film of acousticcoupling fluid or gel as each transducer element 105 moves along acomplex body curvature. The acoustic lens 106 is similar in principle toan optical lens in that the effect of the roller ball 105 on theultrasonic beam is precompensated before passage through the roller ball105.

An embodiment in which a multitransducer element assembly is employed isillustrated in FIGS. 7a and 7b. In this example, three elements, such as123, 124 and 125, are mounted on the tip of each plunger 127, or plunger15 of FIG. 2. Thus, the scanner head 10 becomes an array with three rows(rather than one row) of transducer elements.

The implications and advantages of three rows of transducer elementswill be discussed later when the Multireceiver mode of transduceroperation (as opposed to Fundamental mode) is described.

The mechanical transport system for moving the scanner head down theback is illustrated in FIGS. 2, 3 and 4. Note that the systemimplemented employs a servomotor motor 41 and gear reduction (withinmotor housing) to turn a set of cable drums 47A and 47B. The drums causesteel cables 48A and 48B to move. The scanner head 10 is attached to thecables 33A and 33B such that movement of the cables causes the scannerhead 10 to slide either up or down the transport side rails 33A and 33Bat a rate determined by the speed of motor 41.

A number of alternative transporters for the scanner head may beemployed, for example a servomotor and gear drive which rotate a longscrew shaft positioned midway between the transport side rails 33A and33B. The screw shaft may be attached via a mating threaded collar to therear of the scanner head 10. Thus, rotation of the screw shaft wouldfacilitate movement of the scanner head along the side rails.

Still another alternative method of scanner head transportation is tomount a set of wheels on the transducer array assembly. The transducerarray 70 and wheel assembly would be pressed against the back and movedmanually down the back. The wheels would serve to convert angularrotation of the wheels to linear distance traveled down the back by thetransducer array.

A block diagram of the scanning system is shown in FIG. 11. As discussedabove, the system is microprocessor-based. The specific microprocessingand display system is shown in more detail in FIG. 12i. The consoleelectronics may be mounted on nine printed circuit boards which insertinto console 60 from the rear.

The central processing unit chosen was the Intel 8085 processor chipincorporated on an Intel ISBC 80/30 single board computer. This initself is a relatively powerful 8-bit microcomputing system containing4K of read only memory (ROM) and 16K of random access memory (RAM). Inaddition, an Intel ISBC 116 memory board was included to increase theRAM by 16K. In the discussion which follows concerning the systemoperation, it is emphasized that all activity is under software control.Software design was, therefore, an intimate part of the overall systemdesign. Broadly speaking, the software may be categorized as operationalsoftware or data processing software. Operational software includes allthe necessary computer instructions required to control the scanningoperation, acquire necessary raw echo data, and store this data inmemory. Data processing software includes those computer programs whichoperate on the raw data to provide numerical and/or graphicalcharacterization of the results. Reference to commands or instructionsimplies computer instructions implemented via the microprocessor.

The graphics or display system is configured in such a manner that theface of the 12 inch CRT 65 may be characterized as a dot matrix of512×512 discrete dots each of which may be selectively either lighted ornot lighted. This is particularly well suited to this applicationbecause data in matrix form may set up so that it may be mapped into acorresponding field on the CRT 65. In addition, the system provides thecapability of an eight-level grey scale in the image, i.e. each dot,when turned on, may be set at one of seven levels of light intensity.This was facilitated by interfacing commercially available Matrox MSBC512 graphics printed circuit cards 84A with the Intel ISBC 80/30 system,as indicated in FIG. 12i. In addition, a Matrox MSBC 2480 board 84B wasadded for the generation and display of alphanumeric symbols. The systemalso incorporates an Axiom EX-850 Video Printer 84C so that any image onthe face of the CRT 65 may be turned into hard copy at the touch of abutton. This particular video printer, however, will not reproduceintermediate levels of grey-scale.

Under processor control any one or any combination of the ultrasonictransducers in the array 70 may be selectively chosen to emit or receivesound energy. In the Fundamental mode of operation, however, eachtransducer in sequence is activated to first emit a short pulse of soundenergy and then to receive or listen for returning echoes.

The scanning system may be also operated in a data acquisition modecalled Multireceiver. This mode is designed to enhance the probabilityof capturing target echoes and it will be discussed later.

In the Fundamental mode a set of commands from the microprocessorpresents a transducer transmitter selection code to the 1 of 16 selector72 as well as the received signal multiplexer 73 (FIG. 11). For example,transducer T₀ is designated as the transmitting transducer. TransducerT₀ is then fired by transducer drive circuit 71D (FIG. 12c) viaappropriate control signals to the 1 of 16 selector 72. Immediatelythereafter a transducer receiver selection code is input to themultiplexer 73 to designate which transducer or transducers will listenfor echoes. In the Fundamental mode T₀ would be designated as thereceiver.

Simultaneously with the launching of a sound wave, a set of one or morerange counters 82 are started. The rate of count is controlled by themicroprocessor system clock and is approximately 1.2 MHz in theembodiment described. As echoes are received by the designated receivingtransducer, this reflected sound energy is converted to a very low levelanalog voltage with a fundamental frequency equal to the fundamentalfrequency of the launched sound wave (2.25 MHz). After passing throughthe multiplexer and receiver blocks 73, this analog echo signal isamplified by a factor of 2 to 5 by the linear preamplifier 74.

The preamplifier is followed by a custom-designed nonlinear time-gainamplifier 76 which has a number of controllable parameters. The detailsof this circuit and its features will be explained further below. Thetime-gain amplifier 76 provides a signal gain which increases with time.The time reference for the initiation of this specialized amplificationprocess is keyed from the command to launch a sound wave. As an initialsound wave propagates away from the transducer of origin through thebody tissue, it dissipates or is attenuated. Likewise, any reflectedenergy (echo) is similarly attenuated in the return path. Therefore,since we wish to discriminate echoes on the basis of amplitude, thephilosophy in designing the time-gain amplifier is to compensate forsound energy losses in tissue with respect to time.

The gain compensated echo signal is now fed to the echo discriminatorblock 83. On the front end of the echo discriminator is an RF detectoror full wave envelope detector (FIG. 12d.2). The purpose of thisdetector is to remove the high frequency (2.25 MHz fundamental frequencyplus harmonics) components from the signal. This results in a signalwhich is the envelope of the echo signal. This echo profile or echopattern, therefore, in general, consists of a series of pulses, theamplitude and time position of which contain information about thevarious tissue interfaces and the distance or depth in the overalltissue aggregate at which such interfaces reside.

Following envelope detection, the echo profile signal is fed into avoltage comparator circuit (FIG. 12d.2). The nature of the comparatorcircuit is such that when and only when an input signal exceeds aselected voltage amplitude, the comparator outputs a well-definedvoltage pulse. The output of the comparator provides a "stop" signal forthe range counter (FIG. 12e).

Therefore, in the Fundamental mode of operation, the most rudimentaryecho detection algorithm is designed such that the first echo in time toexceed a preselected amplitude is detected and used to stop the rangecounter 82 (FIG. 12e).

The relative position of the scanner head 10 with respect to the support30 is monitored by a position transducer 79 (potentiometer 50 connectedto the motor drive system) which generates a DC voltage levelproportional to distance of travel of the scanner head 10. This DCvoltage is converted to a digital binary word by the position A/Dconverter 81 shown in FIGS. 11 and 12b.

After sufficient time has elapsed (about 200 μs for 100 mm of range) forthe range counter or counters 82 to contain an appropriate count, theposition of the scanner head is determined by the processor. Immediatelyfollowing this, the data in the range counter 82 is read. The rangecount which resides as the number of counts per unit of system clocktime is used to calculate the "range" or distance from the transducerface to the tissue interface responsible for generating the echo. Thisis accomplished by the equation: Range=round trip distance/2, orRange=(velocity of sound in tissue)×(time to receive echo/2). Using arange counter clock frequency of 1.23 MHz and an average velocity ofsound in tissue of 1540 m/s, this equation reduces to Range=0.63×COUNT,where COUNT is the number in the range counter.

In the discussion below the notation Y(J)·X(I) shall designate a memorymatrix allocated to store "raw" range data. Raw will mean unsmoothed orotherwise unprocessed data. As an example, a range calculation of 30 mmderived from the echoes detected by T₀ transducer at the uppermostposition of the scanner head would be entered in the raw data memorymatrix as Y(0)·X(0)=30.

The process described above is repeated under microprocessor controluntil the scanner head 10 has descended through all the "J" incrementsof interest. The raw range data matrix is therefore filled from thefirst Y(0)·X(0) element to the last Y(479)·X(15) element following theexample set forth. It should be appreciated that the entire process ofsound transmission, reception or retransmission, echo discrimination,and data storage occurs very rapidly relative to the rate of movement ofthe scanner head 10. Thus, the scanner head does not have to start andstop, but rather moves continuously down the back once the scan isinitiated. The processing of this stored data is described later.

An alternative embodiment of the invention includes two range counters82. In this embodiment a detection algorithm may be mechanized in whichtwo range values may be ascribed to the first two echoes to exceedprescribed thresholds. Such an algorithm is useful as a bone edgedetector.

As described, range counter No. 1 (FIG. 12e) begins counting when asound wave is launched from a transducer element. The counter is stoppedby a signal at input YY. The final count in range counter No. 1 isindicative of the range or distance from the transducer to the firsttissue structure of interest nearest the transducer. After themicroprocessor 75 reads range counter No. 1, the microprocessor resetsthis counter by appropriate signals on J1-20 (reset line) and J1-24(strobe line).

The second range counting system (FIG. 12f) and specifically counter 82Ialso begins counting when a sound wave is launched from a transducerelement. If a second more distant tissue structure of interest isdetected, counter 82I is stopped by the presence of a stop signal on YYof FIG. 12f. Counter 82I will not be stopped by the first detected echo,because line XX will not go high (logical "1") to enable a stop signalto be recognized by 82I until a first echo occurs. The contents of 82Ithus represent the range to the second tissue interface of interest, andit may be read by microprocessor 75. Subsequently, range counter No. 2is reset after being read via lines J1-20 and J1-24. In the event asecond echo is not detected, counter 82I will overflow and thusautomatically reset.

Another alternative embodiment includes linear position transducer 20(FIG. 5b) which provides the position of each transducer, such as 28,along the "Z" direction, that is a direction perpendicular to the fieldor plane of scan defined by the "X" and "Y" coordinates referred toabove. This position is fed into the microprocessor to refine the rangevalues or in order to determine the range values with respect to anabsolute plane, rather than in respect to the relative plane of theback. Such absolute range values may enhance the visual reconstructionof the dorsal skeletal structure and thus improve the resolution of thescoliotic curve characterization.

Shown in FIG. 11 is a high-speed A/D converter and memory buffer system85 which is connected by dashed lines to the main scanner system. Thispart of the system is primarily for research purposes and may be brought"on line" as an option. The circuitry for this part of the system isshown in FIGS. 12g.1, 12g.2, 12h.1 and 12h.2 and the characteristics aredescribed below. Since echo patterns are extremely transient in nature,the high-speed A/D converter and memory buffer 85 provide anultrahigh-speed means of examining a designated echo pattern. When inuse the memory buffer is always saving a prescribed number of scan linesor J lines of continuous echo amplitude data. For example, if thestandard echo detection algorithm provides questionable data in someportion of the scan field, the appropriate contents of the memory buffersystem may be interrogated under software control to recreate the analogecho pattern in this specific region of interest. The validity of theecho detection algorithm in this region of question may then beexamined.

A smooth planar surface tends to reflect a sound beam according toSnell's law (i.e., angle of incidence equals angle of reflection). Thus,in such a simple case, the maximum "signal strength" of the echo patternis obtained when the incident beam is perpendicular to the reflectinginterface. In most practical cases, and in particular, with theirregular surface geometry of the bony structure of the ribs and spine,this ideal condition does not exist for all components of the target. Anincident sound beam, although it can be focused, cannot be madeinfinitely narrow and, therefore, at least some minimal energy willreturn to the transmitting transducer unless the target surface has anextremely oblique angle relative to the face of the transducer. Thesystem, when operated in the Fundamental mode of data acquisition,relies on the high sensitivity of the receiving transducer 12 and thegain characteristics of the echo amplifiers 74 and 76 to capture atleast a portion of the reflected energy contained in an echo from bone.

To enhance the probability of receiving echoes from bone returning notalong the longitudinal axis of the sending transducer, the Multireceivermode of operation was devised. In its simplest version, theMultireceiver algorithm is designed to operate in conjunction with asingle row of transducers as shown in FIGS. 3 and 5a. A moresophisticated but more effective technique employs several rows oftransducers as illustrated in FIGS. 7a and 7b.

In the basic Multireceiver algorithm, a transducer (e.g., T₂ of FIG. 5a)launches a sound wave and then the same transducer T₂ listens forechoes. If no echoes are received, T₂ refires, only adjacent transducerT₁ now listens. If still no echo, T₂ refires and the other adjacenttransducer T₃ listens. Following this procedure, the next transducer innormal sequence (namely T₃) fires and listens. If no echo, T₃ refires;T₂ listens. If no echo, T₃ refires, T₄ listens and so on. Because theadjacent transducer elements are intentionally located close together,very little error in calculated range values occur whether the launchingtransducer receives an echo or an adjacent transducer receives an echo.Nevertheless, errors in range values may be minimized by makingfundamental trigonometric calculations which compensate for thedisplacement between the transmitting and receiving transducers.

The Multireceiver algorithm may be extended to operate in conjunctionwith a multirow set of transducer elements as partially indicated inFIG. 7a. Only twelve transducer elements are shown in the figure, butcompatibility with the forgoing example would indicate use of (16×3) or48 transducer elements arranged as suggested in FIG. 7a. In thisexample, the trio of elements T₁, T₁₇, and T₃₃ would be mounted in acommon shoe affixed to a plunger. Note the slant in the orientation ofthe elements as opposed to vertical orientation. This feature allowsminimization of the spacing in adjacent transducers. If transducers T₀,T₁ and T₂ were fired in sequence, there would be significant physicalseparation; however, if T₁₇, T₁ and T₃₃ are activated in sequence withproper adjustment in the J level corresponding to the Y dimension on theback, the physical separation between transducers in the X direction isreduced to zero (or, in fact, could produce overlapping beam widths).

In an extended version of Multireceiver (referring to FIG. 7a), T₁ firesand listens. If no echo T₁ fires again, T₀ listens. If no echo, T₁ firesand T₂ listens. If no echo, T₁ continues to fire and in sequence T₁₇,T₁₈, T₃₂ and T₃₃ would listen. That is to say those transducers"surrounding" the designated firing transducer are given an opportunityto capture an echo.

At any stage in the sequence, a valid echo terminates the iteration oflistening transducers and transmitter control is passed to the nextadjacent transducer, namely T₂. The sequence is then repeated in similarfashion. Consequently, the ability of the Multireceiver algorithm tocapture off axis echoes is effectively extended from one dimension (X)to two dimensions (X and Y). That is, if required, the four transducerssurrounding each "center" transmitting transducer may be designated aslistening transducers.

The main purpose of the echo processing electronic circuits which areunder control of the microprocessor is to detect valid ultrasonic echoesand to calculate the distance from the transducer to the structure thatreflected the incident ultrasonic pressure wave.

In general, echoes will occur whenever the transmitted ultrasoundencounters a bone and muscle (or soft tissue) interface, a muscle andlung interface, or even a skin and muscle interface. The size of theecho depends on several factors; the characteristics of sound (velocityand attenuation) in each medium and the angle of incidence of the soundand the interface.

The scanner head electronics is shown within the dashed lines of FIG.11. The sixteen transducers (shown in FIGS. 2, 4 and 5a) are mountedside-by-side, making up a horizontal array approximately six incheswide.

Each transducer has a separate drive circuit 71D (FIG. 12c) which can beaddressed by the microprocessor in various patterns; the usual patternis to begin at the left and sequentially activate each transducer. Thedrive circuits supply a short, high voltage (200 to 500 volts) pulse tothe transducers. This causes an ultrasonic pressure wave to travel outfrom the surface of the transducer. This pressure wave travels throughbody tissue at a typical velocity of 1540 m/sec and the tissueattenuates it by an average of 2 db/cm.

Echoes produced by bone/tissue interfaces return to the transducersurface and cause an electrical response in proportion to the magnitudeof the echo as has been previously explained.

Immediately after the transducer is activated, it is connected to areceiver and amplifier circuit (FIG. 12c), such that any returningechoes can be amplified and processed further.

The linear preamplifier 74 located on the scanner head 10 provides onlya small amount of gain, but does provide the necessary drive to send thesignal back to the main electronics package 60.

In the circuit of FIG. 12d.1 the nonlinear time dependent gain amplifier76 includes a dual gate field effect transistor (FET) 76B. One gate, 76Eof the FET controls the gain characteristics and the other gate 76F isthe echo signal input. The SIGNAL AMP (back panel adjustment) control76G is connected to the echo signal input gate 76F. By keeping thecontrol gate 76E at a negative potential, the signal on the other gatedoes not appear at the output of the FET. As the voltage level on thecontrol gate 76E increases, the gain of the FET increases until themaximum gain is reached. By changing the voltage level on the controlgate 76E of the FET it is possible to have a time of zero gain and atime when the gain is increasing linearly towards the maximum gain.Ideally, the gain would never be less than one, however, because oftransducer ringing, it is necessary to have zero gain for severalmicroseconds following the activation of the transducer. By controllingthe time until maximum gain is reached corresponding to a depth of oneto five centimeters the attenuation of the signal by tissue can becompensated.

Of the seven external back panel adjustments, four are related to thecontrol gate signal. These four are RAMP OFFSET 76H, DELAY 76I, SEGMENT1 76J, and SEGMENT 2 76K. These potentiometers are located in thecircuit of FIG. 12d. The RAMP OFFSET 76H adjusts the negative potentialon the control gate 76E. The DELAY 76I adjusts the time at which theamplifying process begins relative to the launching time of a sound wave(time zero). The profile of the time-gain characteristic may be regardedas having three segments. The slopes of the first and second segmentsare determined by the settings on the SEGMENT 1 76J and SEGMENT 2 76Kcontrols respectively. The gain of third segment is inherently themaximum gain available from the amplifier. The WINDOW (bank paneladjustment) control 76L sets the maximum allowable time foramplification.

The time-gain amplifier described above plays an important role indistinguishing echoes from the ribs and spinal column from other echoes,in one aspect of the invention. A time-gain amplifier is an amplifier inwhich the gain can be changed over a specified time period. Anultrasound signal traveling through tissue suffers approximately 2db/cm. attenuation, thus the amplifier may be adjusted to compensate forthe attenuation by B increasing its gain at a rate of 2 db/13 μsec (thespeed of sound in tissue results in a round trip time of 13 μsec, i.e.to travel 1 cm. and back).

However, for the purpose of detecting echoes from ribs and vertebrae,the optimal amplifier gain versus time curve is not simply one ofincreasing gain at a 2 db/13 μsec rate. The following specificcharacteristics make the amplifier time-gain characteristics closer tothe ideal for detecting echoes from ribs and the spinal column:

(1) There is an adjustable time of zero gain (Delay adjust 76I) whichcorresponds to a depth of from 0 to 1 cm. of tissue. This allowsadjustment of the instrument to eliminate ringing artifact from thetransducer pulse and also any false signals that might be generated atthe transducer/skin interface.

(2) There are controls for modifying the shape of the time versus gaincurve during tne time from 13 μsec to 130 μsec corresponds to a tissuedepth of from 1 cm. to 10 cm. These controls enable a piecewiselogaritnmic gain characteristic to be constructed over various portionsof the 13 to 130 μsec time span. In the present implementation two suchcontrols are provided; they are Segment 1 (76J) and Segment 2 (76K).Clearly any number of such controls as may be found necessary toconstruct an appropriate gain characteristic in other embodiments may beused.

As described below, in an optional embodiment the invention using ahigh-speed analog-to-digital converter, the gain changes are done in aclosed loop fashion under the control of the microprocessor. Themicroprocessor increases the gain in an area where it expects echoes anddecreases the gain where none are expected. The areas where echoes areexpected (i.e. have a higher probability of occurring), may be "learned"by the computer from one or several previous scans at a slightlydifferent anatomical position or by repeated scans in the same locationwith different gain versus time profiles. In other words, in thisembodiment the ultrasound time-gain amplifier is "trained" for optimalamplification.

The RF detector (FIG. 12d.2) full wave rectifies the echo and appliesthis rectified signal to the comparator also shown in FIG. 12d.2. Thecomparator has an adjustable threshold setting 83D called DETECTORTHRESHOLD (back panel adjusment). Thus, only echoes above the thresholdare detected.

When an echo is detected, the range counter of FIG. 12e is stopped. Thecount that has accumulated corresponds to the range (or depth) of thestructure that produced the echo. The resolution of the range counter inthe preferred embodiment is 0.6 mm.

A second counter which is indiCated in FIG. 12f can also be started whena transducer is fired. This gives the capability of calculating therange for the first two echoes that exceed the comparator threshold.

Not every transmission produces an echo. There are many possible reasonsfor not getting an echo large enough to trigger the comparator. Thetarget may have been at such an angle to the incident sound wave thatthe echo may not return directly to the detector, or there may not havebeen a target within the maximum allowable range of 150 mm. Theapplication of the Multireceiver mode in alleviating some of theseproblems has been discussed.

In order to examine the analog echo signal in the event that echoes arenot detected, a high-speed analog-to-digital (A/D) converter (FIGS.12g.1, 12g.2, 12h.1 and 12h.2) can be brought on line under softwarecontrol. The A/D converter 85B employed is a TRW model TDC1007PCBmodule. The 8-bit A/D converter output qoes to an array of shiftregisters, such as 85C, which can hold 1024 8-bit conversions of theanalog echo signal. The conversions are made at a 10 MHz rate;therefore, 102.4 microseconds of data can be held in the shiftregisters. The data can then be automatically clocked out of the shiftregisters at a slower rate providing a data expansion capability.

Alternatively, the data in the shift registers can be stored in themicroprocessor memory 75A and 75B (FIG. 121). Each 100 microseconds ofdata would require 1K of memory.

Examination of this data allows a more desirable detector level settingor gives insight into a more intelligent nonlinear gain curvecharacteristic. To enhance the probability of detecting echoes thedetector level may be adjusted dynamically. For example, if an echo isnot detected after a transmission, the detector sensitivity may beincreased and a second transmission made. If an echo is still notdetected, the iterative process of detector level shifting andretransmission could be continued.

The position A/D converter 81 (FIG. 12b) provides a signal proportionalto the vertical position of the scanning array. When the appropriatevertical distance has been scanned, the microprocessor 75 will stopactivating the transducers 70 and inform the operator that the scan iscomplete.

The range data from each of the echoes received during a scan are storedin the microprocessor's memory 75A and 75B. This information isavailable for future processing and is used to generate a display thatshows the spine and ribs.

DATA ACQUISITION AND PROCESSING

FIG. 13 is a flow diagram indicating the progression of scanner startup,data acquisition, and data processing. Certain optional decisionsselected via the keyboard 80 are indicated which, in general, yieldintermediate displays and supplemental results on route to the finalcharacterization of the curvature of the patient's spine.

After the instrument is powered up, the patient's name and/or a filenumber is entered. For a returning patient, a summary of the results ofthe previous evaluation is read from floppy-disc memory 75D andpresented on the CRT 65 of the console 60. For a new patient, a new fileon magnetic disc 75D would be created and the relevant aspects of thepatient's history are entered. When the patient is prepared for thescan, a command at the keyboard 80 causes the scanner head 10 toautomatically seek the "ready" position along the transport rails 33Aand 33B. Subsequently, the mode in which the transducers 12 are tooperate is selected. The scanner head 10 is then pressed against thepatient's back such that the individual transducer elements 12 are inpositive compression against the patient's skin 11. The transportsystem's reference points, cervical 31 and sacral 32, are correctlyaligned on the patient's back 11 by palpation.

A keyboard command, or alternatively, momentary depression of a remotestart button 64 (FIG. 1) mounted on the transport system 30 initiatesthe scanning procedure. As the scan is progressing under softwarecontrol, a real time display is presented on the CRT 65 of the systemconsole 60. This shall be known as the Basic XY display. A portion ofthe 512×512 dot matrix CRT field is selected to be a proportioned scalereplica of the XY field of scan on the back 11 of the patient.Therefore, in the Fundamental mode of operation previously described afield of 16 pixels by 480 pixels represents the back 11 of the patient.At the beginning of the scan this CRT field is darkened. The Y(J)·X(I)memory matrix which is used to drive the CRT pixel field is initializedwith all elements set to range values of 150 mm. A range value of 150 mmis arbitrarily chosen as the maximum range value of any relevance forthe purpose of evaluating spinal curvature. Therefore, the "background"value for this imaging becomes 150 mm. As the scan proceeds, eachcalculated range value is tested against a criteria of being between(but not equal to) 0 mm. and 150 mm. If this condition is met, thememory value of 150 is replaced with the new range value and thecorresponding pixel on the screen is lighted.

In practice the rate of travel of the scanner head 10 down the back 11of the patient is very slow compared to the rate of firing of thetransducers 12. A typical scan requires a half minute to a minute tocomplete, whereas the firing and listening sequence of 16 transducers ata particular J level may be completed in 30 ms to 100 ms. It wasdetermined experimentally that it was desirable to have each transducer12 interrogate the same elemental region of the field of scan more thanonce so as to enhance the probability that relevant echoes would bereceived. Therefore, the system is adaptable so that there are multipleopportunities for acquisition of echo data and hence tne replacement ofthe initialized range values (150 mm.). A software option is discussedbelow for averaging of multiple attempts or the presentation and displayof tne contribution to end results from multiple attempts. Once thebackground value of 150 mm. is replaced, it was found desirable to"lock-out" further attempts to change the range value during the samescan.

The echo signal amplifiers 74 and 76 and detection system 83 weredesigned and adjusted so that there is a high probability of triggeringthe discriminator 83 and hence producing a valid range value at eachdiscrete element in the field of scan even though the transmitted soundwave does not encounter bone. This occurs because a large portion of thescan field is in the thoracic region. In this region the lungs andpleural sac of the lungs are in close proximity to the ribs. In viewingthe patient from the back, the ventral aspect of the ribs is inapposition with the pleural sac. Experimentally, it was found thatsignificantly strong echoes are returned from this pleural tissueinterface between the ribs. Importantly, the average range valuesreturned in the intercostal spaces are larger than those range valuesreturned from the dorsal aspect of the ribs. The average difference isthe thickness of a rib (5 mm to 10 mm), and this formulated the basis ofthe software which extracts rib from lung, i.e., the Bone/LungClassifier.

Upon completion of the scanning operation, the Y(J)·X(I) data matrix isfilled with raw data. This data is then copied into the Y₁ (J)·X₁ (I)data matrix. The data in the Y₁ (J)·X₁ (I) matrix is processed andchanged while the Y(J)·X(I) matrix preserves the raw data which iseventually transferred to magnetic disc storage 75D under the patient'sraw data file. Next, the Y₁ (J)·X₁ (I) data is subjected to a routinesmoothing operation. The data is smoothed down each "I" column. Thisdata may then be displayed as illustrated in FIG. 14.

FIG. 14 may be considered a composite display of the results obtainedfrom each of the "N" individual transducers 70 (sixteen in the exemplaryembodiment). Each column T₀ through T_(N-1) shows a range profile orrange "signature" for each transducer 12 as it traversed the back 11from J_(begin) to J_(end). In each column of FIG. 14 the line to theleft of each signature is the zero range reference line which is theface of the transducer 12. The primary concept to be conveyed by FIG. 14is that as the tranducers move down the back, range signatures aregenerated which have geometric attributes germain to the anatomy of theskeleton underlying the transducers. For example, in FIG. 14, the ribsappear as "humps" with rounded or flattened tops. Intercostal spaces arerelatively straight lines connecting the rib humps. More triangular orjagged peaks are characteristic of spinal components--primarily spinousprocesses and certain aspects of the transverse processes.Interestingly, it was determined that there is a high probability thatthe nonsporadic absence of echoes in a region is the result of incidentsound wave striking spinal components. The manifestation of this wouldbe breaks in the range signatures of FIG. 14. This phenomenon is due tothe complex geometry of the spinal components and in particular theobliqueness of the surfaces of the spinal components relative to theface of the receiving transducers. In these situations, the probabilityof echoes returning directly to the transmitting transducers is lowered.Nevertheless, recognition of this phenomenon is useful in the patternrecognition and classification of skeletal components.

Using this information, then, it is possible to implement the Bone/LungClassifier indicated in FIG. 13. In conjunction with this dataprocessing, the Spine/Rib Classifier is implemented. The predominatefeature of this algorithm is the extraction of those range valuesassociated with the peaks or crests of the rib humps and spinousprocesses from the range signatures of FIG. 14. A display of the resultsin the same format as in FIG. 14 yields the display illustrated by FIG.15. Any identification of the tips of the spinous processes (illustratedas squares) results in the memory storage of tne associated range valuesand the (J, I) coordinates for later use in the assessment of vertebralrotation.

Next, the data points indicated in FIG. 15 are processed such that therib crests (illustrated as circles) are effectively connected. Thealgorithm for this is referred to as the Rib Crest Tracker in FIG. 13.These results may be optionally displayed in the format of the Basic XYdisplay wnich is illustrated in FIG. 16. As previously stated, thisdisplay is scaled in the X and Y directions proportional to the X and Ydimensions of the patient's back. Hence, this display indicates therelative position of ribs as projected on the XY plane. The relative"angles" of the ribs and their relative parallelism is indicative ofspinal curvature. Note, for example in FIG. 16 the locus of points whichare connected on the left converge to the left and the locus of pointswhich are connected on the right diverge to the right. This nonsymmetryis indicative of a clinical situation of abnormal lateral spinalcurvature coupled with rotation of the vertebrae. On the concave side ofa curve in the spine, the ribs tend to converge or close togetherwhereas on the convex side of the curve the ribs diverge or become morewidely separated.

A Spinal Boundary Constructor algorithm is next implemented. The resultof lighting all pixels representing the boundary of ribs and spine onthe left and right side of the spine produces the display shown in FIG.17. The next step involves implementing an algorithm which is referredto as a Medial Axis Transform of the spinal mass. The objective of theMedial Axis Transform is to find the "best" center line or medial axisthrough the two-dimensional irregular spinal mass shown in FIG. 17. Theresult of performing this operation is the solid line 94 in the displayof FIG. 18. The solid line 94 thus becomes a single line representationof the lateral curvature of the spine. The X and Y coordinates of thisline are stored in memory and may be used to mathematically characterizethe curved spine as any curved line may be characterized. Also, theresults may be output in the form of hard copy graphics on the CRT 65 orprinter 84C. By making a transparency of the hard copy, the results ofsubsequent evaluation may be compared by overlaying the transparencies.

The broken line 95 indicated in FIG. 18 is a display of results relatedto vertebral rotation. Most often in the clinical examination ofscoliosis it is found that the vertebrae tend to rotate with spinousprocesses and pedicles deviated toward the concave side of the curve.The broken line 95 of FIG. 18 is thus a display in the XY plane of thelocus of the tips of the spinous processes which is derived from thedisplayed data (squares) of FIG. 12. In a normally "straight" spine thesolid and broken lines 94 and 95 of FIG. 18 would be essentiallycoincident. Consequently, a measure of the noncoincidence of the twolines of FIG. 18 is, in essence, a measure of the degree of rotation ofthe spine associated with the scoliosis.

The data processing is concluded as indicated in FIG. 13 by the storageof the results of the scoliotic examination on the patient's permanentfile residing on magnetic disc 75D. The file is then closed. The systemmay then be initialized for the next examination.

SOFTWARE

The software which was developed for the scanning system was writtenexclusively in the Intel PLM-80 language. Listings of all the relevantprograms developed and debugged appear in the Appendix. A knowledge ofPLM-80 coupled with numerous program comments in the listings allow thereader to follow the programs quite readily. To further aid this processand to enhance the appreciation of how the various algorithms weremechanized, a brief discussion of the software follows.

In the discussion which follows there will be reference to the names ofprograms and to the names of procedures. A modular approach to softwaremanagement was employed. This means that a number of programs werewritten which, in turn, contain numerous procedures or subroutines. Thisis to be contrasted with one huge program. Modular programmingfacilitates changes and additions because only the particular programcontaining changes need be compiled following the changes. All programsare effectively joined into one large program by the process of"linking" which is done automatically on command to the microprocessordevelopment system.

SCAN21.PLM is the Scanner's main program, or MAIN$MODULE. Main in thesense that this program initializes a number of variables and preparesthe system for use when the power is turned on. SCAN21 perpetuallyinterrogates the Scanner keyboard 80 to see if any commands have beenentered. When selected keys are pressed, SCAN 21 makes the appropriatecalls (or jumps) to other routines in the system. The listing ofSCAN21.PLM (see Appendix) includes as comments a menu of choices forkeys. For example, to initiate a new scan, either keys 1 (callsBASIC$SCAN$PROCEDURE), 8 (calls MULTI$RECEIVER$PROCEDURE), or 9 (callsMULTI$CENTER$FIRE$PROCEDURE) would be pressed.

SCAN21.PLM also contains procedures for copying or transferring thecontents between the various data matrices which were established,namely Y(J)·X(I), Y₁ (I)·X₁ (I), and Y₂ (J)·X₂ (I).

The SCAN1O.PLM file is referred to as the FUNDAMENTAL$XY$SCAN$MODULE.This module contains the procedures XY$REG, DISPLAY$1, DISPLAY$1A,BASIC$SCAN, and RESCAN.

BASIC$SCAN provides the software for positioning the scanner head 10 atthe ready position. Then all range values in the Y(J)·X(I) and Y₂ (J)·X₂(I) matrices are preset to 150. BASIC$SCAN starts the descent of scannerhead 10 and a loop sequentially transfers control from transducer totransducer across the array. At each transducer, such as 12, flags areexamined to determine the receiving mode and flags are set to later beexamined by an XY display routine to determine which pixels in the scanfield should be lighted.

DISPLAY$1 and XY$REG work together to locate the pixel in the XY fieldto be lighted or not lighted as determined by information in the datamatrices. DISPLAY$1A may be called from other programs to turn offpreviously lighted pixels.

RESCAN simply reconstructs the Basic XY display based upon the mostrecent scan whenever it is called. The original XY display isconstructed in real time as the scan head moves. RESCAN is used torecall the XY display after it is erased from CRT 65.

SCAN12.PLM is the MULTI$RECEIVER$SCAN$MODULE and it contains theprocedures MULTI$RECEIVER and MULTI$CENTER$FIRE. MULTI$RECEIVER containsthe software needed to control the transducers, such as 12 in a fashionsuch that reception of incoming echoes may occur on either the right orleft transducer adjacent to the designated transmitting transducer. Thestructure of the MULTI$RECEIVER algorithm truncates the iterativeprocess of transmitting with a designated transducer and listening withadjacent transducers as soon as a valid echo (range value less than 150)is detected. Additionally, echoes detected by the "center" or designatedtransmitting transducer may be separated from those subsequentlydetected by the "adjacent" transducers.

MULTI$CENTER$FIRE is a routine which will fire the "center" transducerfor a preselected variable number of attempts at a particular J value (Ycoordinate) in the field of scan in an effort to obtain an acceptableecho before it stops trying and passes control back to the callingprogram.

Referred to as the ACTIVATE$TRANSDUCERS$MODULE the F5.PLM programcontains the procedures FIRE$RECEIVE$SELECT,FIRE$CENTER$RECEIVES$CENTER, FIRE$CENTER$RECEIVE$RIGHT, andFIRE$CENTER$RECEIVE$LEFT. FIRE$RECEIVE$SELECT controls the switchinglogic to implement a code which is sent to the 1 of 16 selector 72 andreceived signal multiplexer 73 for designating an active (transmittingand/or receiving) transducer and then applies a trigger pulse to firethe selected transmitting transducer via tranducer drive circuit 71D.The other procedures in this module perform functions exactly as theirrespective names imply.

The R4.PLM program is referred to as the DETERMINE$RANGE$MODULE.Whenever the procedure DETERMINE$RANGE is called, the count in the rangecounter 82 is read and a calculation is made to determine thecorresponding distance in millimeters to a target component. Presently,this calculation is based upon an average velocity of sound in tissue of1540 m/s.

CTR70.PLM is the YZ$BY$COLUMN$DISPLAY$MODULE and contained within it arethe procedures BOUNDARY$LINES, COLUMN$MIN$MAX$SEARCH, YZ$DISPLAY,YZ$DISPLAY$LEFT, YZ$DISPLAY$CENTER, YZ$DISPLAY$RIGHT, andYZ$DISPLAY$TWO. In general, the purpose of this module is to generate adisplay on the CRT 65 which is a composite plot of Z (range) valuesversus Y position for each transducer element (T_(I) column).BOUNDARY$LINES divides the face of the CRT 65 into columns separated bydashed vertical lines which are equidistant apart. Each boundary linegives a zero reference for the corresponding position of the face oftransducer 12 in the Z dimension. YZ$DISPLAY keeps track of the columninto which a particular range value should be plotted and examines flagswhich indicate whether results from "single receiver", "multireceiver",or a composite of the two should be presented. The rest of theprocedures select and display either a left, right, or center section ofthe transducer columns. YZ$DISPLAY$TWO compresses the results of left,center and right into one picture, but boundary lines between columnsare dissolved.

CRT70.PLM also contains a procedure called COLUMN$MIN$MAX$SEARCH. Thisroutine implements a search through the raw data matrix I column by Icolumn. The output of this routine results in construction of threeone-dimensional arrays which contain the minimum value, maximum value,and difference between min and max for each I column.

Known as the ISOMETRIC$DISPLAY$MODULE the CRT51.PLM file containssubroutines which produce an isometric three-dimensional box or framearound the plotted data. The subroutine END$POINTS$1 locates each datapoint in the three-dimensional space. The procedure requires notrigonometric function calculations. Instead the program was written toemploy 4, 12, 13 standard triangles.

Positioning is then based on the concept of similar triangles. Aprocedure called CONNECT$POINTS$1 serves to draw line segments betweenthe data points. All line segments are drawn within a specified J value,i.e., for a given Y coordinate data point, a line segment is drawn tothe next adjacent data point with the same Y coordinate. The programallows lines to be drawn only at specific intervals of J values. Themethod of geometry allows only three possible vector directions for linesegment construction, namely zones of "vector 0" (0° to 90°), "vector 1"(180° to 270°), and "vector 2" (270° to 360°). The proceduresISOMETRIC$DISPLAY and ISOMETRIC$DISPLAY$TWO are similar in principle,but ISOMETRIC$OISPLAY$TWO plots data points (end points) for each valueof J rather than intervals of J, and further, the end points are notconnected. Thus, the relationship of data points tends to be withrespect to X values rather than Y values. In other words,ISOMETRIC$DISPLAY produces line segments for designated J values whileISOMETRIC$DISPLAY$TWO tends to produce line segments for designated Ivalues.

The GRY3.PLM program is called the GRAY$SCALE$MODULE and it containsprocedures referred to as MIN$MAX$SEARCH, GRAY$LEVEL$SET, andEIGHT$LEVEL$GRAY. GRY3.PLM develops an XY display of range values in aneight-level gray scale. The format is identical to the basic DISPLAY$1routine except that the light intensity of each lighted pixel isindicative of the relative magnitude of the range value driving therespective pixel. The brightest pixels are the smallest range values. Acall from MAIN$MODULE for EIGHT$LEVEL$GRAY initiates the process. Thealgorithm employs "auto-scaling." That is, the difference between thelargest range value and the smallest range value is factored intoestablishing the scale as opposed to assigning absolute range values toparticular light intensities. MIN$MAX$SEARCH locates the minimum valueand the maximum value of all range values in the Y₁ (J)·X₁ (I) processeddata matrix. Then the difference between the min and max is divided intoeight bands. These partition ranges are referred to as slice 0 throughslice 7.

GRAY$LEVEL$SET then evaluates each range value and assigns a gray levelto it. The appropriate pixel in the XY field corresponding to the Zvalue or range value in question is located and turned off. Then it isturned back on at a light intensity proportional to its assigned level.The equation

    MODIFIED$RANGE$PARTITION=(RANGE$SPREAD-(N$PARTITIONS*RANGE$PARTITION))/7

where RANGE$SPREAD=MAX$VALUE-MIN$VALUE andRANGE$PARTITION=RANGE$SPREAD/7 determines the width (range of values)contained within each level of gray. This equation was implementedbecause of the nonuniform distribution of range values. The majority ofvalues cluster more toward the minimum rather than the center or themaximum values. Therefore, as the N$PARTITIONS factor (which is normallyset at two) is increased, the width of each gray band shrinks, thusyielding more resolution and the more the entire gray scale is shiftedtoward the minimum. As the RANGE$SPREAD is increased for a givenN$PARTITIONS, each gray band widens.

A more elaborate, and perhaps better technique, would be to perform astatistical analysis of range data thus finding the mean and standarddeviation. The gray scale could then be positioned optimally within thisdistribution. The gray scale image would, however, develop dramaticallyslower.

The CLASS1.PLM program is referred to as BONE$LUNG$CLASSIFIER$MODULE.The procedures within this module are JBAND$MIN$MAX$SEARCH, JGAP$TEST,INTP$RANGE, BONE$LUNG$ONE INTERPOLATE, and BONE$LUNG$TWO.

BONE$LUNG$ONE and BONE$LUNG$TWO implement algorithms which have beendiscussed to some degree. The goal is to segregate range valueattributable to bone from range values largely attributable to lungs orplueral sac membrane. BONE$LUNG$ONE was developed first and operates inthe following manner. Each I column in the Y₁ (J)·X₁ (I) processed datamatrix is searched for a minimum and maximum value. Then a "decisionline" is constructed somewhere between these limits. In the language ofthe program, the choice of a value for the variable DF determines wherethis decision line is drawn. Range values less than the decision valuewere classified as bone. If DF=4, for example, the decision line isdrawn midway between the min. and max. If 0≦DF<4, then the decision linewas shifted toward smaller values of bone. Likewise, if 4<DF≦8, then thedecision line is shifted toward larger range values. In general, adifferent decision value is selected for each I column in BONE$LUNG$ONE,but the decision is static for the column.

In BONE$LUNG$TWO, however, a decision value is dynamic in the sense thatit is computed for each J value down the column. At each J value or "JPoint" there is a look-ahead and a look-back for a total span of "JBand." The min and max values of range are found in the current J Band.Then the decision rule is applied as in BONE$LUNG$ONE. A value of 20 forJ Band seemed optimal and this is primarily due to the fact that the ribspacing in the experimental data was about equivalent to twentyincrements of J.

INTERPOLATE is called upon to fill small gaps in the range signaturesdown each I column. The routine is written such that when a gap in datais encountered, the width of the gap is tested (by call of JGAP$TEST)against a criteria which can be experimentally varied. For example, ifthe gap is no greater than five increments of J, then a call is placedto INTP$RANGE. INTP$RANGE then performs a linear interpolation to fillthe gap with data.

SM1.PLM is the RANGE$DATA$SMOOTHING$MODULE and it is implemented by acall from the main program to the procedure NONWEIGHTED$SMOOTHING. Thepurpose of this routine is to smooth or average the range data down eachI column thus producing a more attractive range signature containingless noise. For each J value in a column, 2K+1 values of range areaveraged, where K is the number of J values on each side of the center JPoint. For this procedure, data is input from the Y₁ (J)·X₁ (I) matrixand "smoothed" data is output to the Y₂ (J)·X₂ (I) matrix.

RIB1.PLM is a program to evaluate a concept for identification andremoval of rib data from the general data field. This program was onlypartially successful in that some of the non-spinal data which could beattributed to ribs was removed. Therefore, there are some attributes tothe algorithm which could be included in an extensive rib removalalgorithm. It should be noted that the illustrative program operates ondata with fifteen columns, i.e, fifteen transducers are involved in dataaccumulating, rather than sixteen transducers as in other illustrations.

There are four subroutines in the present RIB1.PLM program. They areCENTER, RIB1$STRIP$ONE, RIB1$STRIP$LEFT, and RIB1$STRIP$RIGHT. A callfrom MAIN to RIB$STRIP$ONE initiates the process. RIB$STRIP$ONE setsvalues on several variables, and then in succession calls CENTER,RIB1$STRIP$LEFT, and RIB1$STRIP$RIGHT. CENTER simply moves down (J=0 to479) through the center of the raw data field (specifically columns I₆,I₇, I₈) and copies these range values to the processed data matrix Y₁(J)·X₁ (I). RIB1$STRIP$LEFT and RIB1$STRIP$RIGHT implement an algorithmwhich is based upon a rib model stating that range values for rib willincrease as the transverse distance from either side of the spineincreases. This is an oversimplified model, but it is at least partiallytrue for regions along a rib.

RIB1$STRIP$LEFT works from the left toward the center of the data,whereas RIB1$STRIP$RIGHT works from the right toward the center. For agiven row or J line, each range value in that row (i.e., I₀ through I₅on the left, and I₁₄ through I₉ on the right) is compared to each valuein an adjacent "element field." The dimensions of the field are set bythe variables J$FIELD and I$FIELD. Best described by example, thealgorithm was tested with a field of I$FIELD-2 (width) by J$FIELD-5(length). The test value of Y(5)·X(0) would be compared with each valuein the ten element field Y(J)·X(I) where I=1, 2 and J=0, 1, 2, 3, 4. Ifthe test value was greater than or equal to any element in the field,then the test value was considered rib and was discarded. The test valuewould then become the next value over (increment I on left) in theparticular J line and the elemental field would be shifted one column tothe right (left for RIB1$STRIP$RIGHT) but still maintaining the samefield dimensions. After completing the current J line, the identicalprocess would be repeated for the next J line down.

It might be predicted that perhaps the only region of the rib where thisalgorithm would work well would be those portions under end transducerson the extreme right and left. In this region the ribs begin to curveanteriorly toward the thorax. There was significant removal of dataimmediately adjacent to the spine (e.g., transducers T₄, T₅ and T₉,T_(1O)). One interesting possible explanation is that the boundarybetween rib and spine is partially being detected. Viewing a transversesection of the thorax in the vicinity of the junction of the transverseprocess to the rib known as the costotraverse articulation there is a"step." In viewing the left side of the spine it is found that the leftside of this step is rib. This would result in a data point of greaterrange value when compared to the right side of the step which would beconsidered a spinal component.

The UPOS.PLM program contains the software to run an analog-to-digitalconverter connected to the scanner head transport system 30. A call tothis program produces a digital number (J value) which defines thecurrent position of the scanner head 10.

The CLEAR2.PLM files contains instructions required to erase the face ofthe CRT 65.

There has been described a novel system for ultrasound scanning whichprovides a method and apparatus for ultrasonic imaging of portions ofthe skeleton, and is particularly suited for detecting the spinalcurvature that is indicative of scoliosis. While the invention has beendescribed in connection with a single preferred embodiment for theentire system and a number of alternative embodiments for particularparts of the system, one skilled in the art will appreciate thatnumerous other embodiments of the entire system and further alternativeembodiments of various parts of the system and departures from theparticular embodiments and alternative embodiments shown may be madewithout departing from the inventive concepts. For example, a widevariety of different scanner heads, scanner head transport systems, andcomputer control and processing systems and display systems and softwaremay be used while still employing the inventive concepts. It istherefore to be understood that, within the scope of the appendedclaims, the invention may be practiced other than as has beenspecifically described.

What is claimed is:
 1. An ultrasound scanning system for skeletalimaging of a back comprising:an array of ultrasound transducers forgenerating an ultrasound signal, for receiving an ultrasound signal, andfor producing an electrical signal representative of said receivedultrasound signal; means for providing a range signal representative ofthe distance from each transducer of objects interacting with saidultrasound signal; means for producing a position signal representativeof each transducer position on the back; means responsive to said rangesignals and said position signals for differentiating pleural sac andlung tissue from skeletal structure; means for producing a profileshowing range as a function of position; means for identifying locationson said profile indicative of said skeletal structure; and meansutilizing said identified locations for providing a displayrepresentative of said skeletal structure.
 2. A system in accordancewith claim 1 wherein said means for differentiating comprises means foridentifying positions at which said range signal changes significantly.3. A system in accordance with claim 1 wherein said transducer means forproducing an electrical signal includes a time-gain amplifier having atime versus gain characteristic selective of signals representative ofskeletal structure.
 4. A system in accordance with claim 3 and furtherincluding means for adjusting said time versus gain characteristic.
 5. Asystem in accordance with claim 4 wherein said means for adjustingoomprises a means for separately adjusting the time versus gaincharacteristic in each of a plurality of time ranges following thegeneration of an ultrasound signal.
 6. An ultrasound scanning system asin claim 4 wherein said means for adjusting comprises a means forconstructing a piece-wise logarithmic gain characteristic over a timespan following the generation of an ultrasound signal.
 7. An ultrasoundscanning system as in claim 4 wherein said means for adjustingincludes:memory means for storing a pattern of skeletal structure from afirst scan; control means responsive to the memory means forautomatically adjusting, during a second scan, said time gaincharacteristic for signals representative of a spinal column and ribs.8. The ultrasound scanning system of claim 1 wherein the means forproviding a display includes means for displaying in two dimensions anindication of each location at which each transducer encountered a ribcrest and a second indicator for each location at which each transducerencountered a spinal process so that rib crest locations for each ribare traced to obtain a rib layout and spinal process locations aretraced to obtain a spinal layout.
 9. A method of skeletal imagingincluding the steps:directing ultrasound signals through a back of abody and receiving said ultrasound signals with an ultrasound transducerwhile scanning said transducer over said back and detecting the positionof said transducer with respect to at least one predetermined referencepoint along a spine to produce range information correlated withtransducer position information; utilizing said range and transducerposition information to produce a profile representing range as afunction of position; differentiating first points on said profilecorresponding to skeletal structure from second points corresponding tointercostal pleural sac tissue; producing a skeletal imagerepresentation utilizing said first points; identifying third pointscorresponding to sides of spinal processes; and using said third pointson said profile to detect vertebral rotation.
 10. A method of skeletalimaging including the steps of:directing first ultrasound signalsthrough a back of a body and receiving said ultrasound signals with anultrasound transducer while scanning said transducer over said bodyportion and detecting the first position of said transducer with respectto at least one predetermined reference point along a spine to producefirst range information correlated with transducer position information;utilizing said range and transducer position information to produce afirst profile representing range as a function of position; storing thefirst profile of skeletal structure based upon the first ultrasoundsignals; directing second ultrasound signals through the back of thebody; automatically adjusting, based upon the first profile, a time-gainamplifier to increase gain in areas of expected spinal structure;receiving the second ultrasound signals with the ultrasound transducerwhile scanning the transducer over the body portion and detecting thesecond position of the transducer with respect to the predeterminedreference point to produce second range information correlated withsecond transducer position information; utilizing said second range andtransducer position information to produce a second profile representingrange as a function of position; differentiating first points on saidsecond profile corresponding to skeletal structure from second pointscorresponding to intercostal pleural sac tissue; and producing askeletal imaging representation utilizing said first points of thesecond profile.